Wire versus Tube:  Stability of Small One-Dimensional ZnO Nanostructures

This paper presents first-principles calculations for ultrasmall ZnO one-dimensional nanostructures. The calculations were done on ZnO nanowires and single-walled nanotubes with n atoms per periodic unit, where one periodic unit is made up of two ZnO layers. The calculations show that, for small n, a single-walled nanotube has lower energy than a nanowire. A crossover point near n = 38 is predicted. Vibrations and vibrational entropy of competing structures is discussed.